“There is nothing wrong with the evangelical church in North America that a good dose of trinitarian theology, if absorbed into the bloodstream of the body of Christ, could not cure.” So writes Kevin Vanhoozer in his blurb to Fred Sanders's The Deep Things of God: How the Trinity Changes everything. Is that true? If so, how does it actually happen?

In The Deep Things of God, you write that among evangelicals the Trinity tends to be “taken for granted rather than celebrated and taught.” Why?

Evangelicals tend to be Bible people, who prefer to stick close to the language of Scripture itself when possible. Often while the doctrine of the Trinity is biblical, it's not a doctrine that God chose to deliver to us ready-made in the words of Scripture. We don't find there the key terms (Trinity, person, essence, relation—even the word three, if we're being that literal). We don't get a chapter-length argument from Paul saying something like, “Now concerning the divine nature and the three persons, brethren, I would not have you ignorant.” You can spend a long time under solid, biblical preaching, and not hear the word Trinity. But you'll be hearing all the actual content of the doctrine: the unity of God, the deity of Christ, the personal distinctions among Father, Son, and Holy Spirit, and so on.

But even when all the parts are there, something can be missing. And often that something is an overall grasp of the big picture, an ability to see how the parts of biblical revelation go together to convey this self-revelation of God as Father, Son, and Holy Spirit. Whenever we think big about the Bible's message, or go deep into the gospel message, we will inevitably dig down to the trinitarian bedrock.

How might a deeper understanding of the Trinity enrich our worship and spirituality?

Much in every way! Coming to understand the doctrine of the Trinity can have a catalyzing effect on every area of Christian thought and life. What we often experience as a disadvantage of the doctrine—that it's so dense with information and so mind-blowingly large—quickly converts into an advantage once you're on the inside of it: it's a doctrine with implications for the whole framework of Christian thought and life.

The first thing an increased understanding of the Trinity will affect is how deeply we understand Scripture. Taking this doctrine seriously will almost immediately improve your Bible reading, as it lights up passage after passage of Scripture.

One example is in the Bible's teaching about Jesus. The New Testament constantly emphasizes not simply the deity of Christ, but also his sonship. If you're reading with a vague and haphazard trinitarianism in the back of your mind, you'll be too easily satisfied with the thought that Jesus is merely God. But with a more sharply focused trintiarian understanding, you'll pick up on the fact that Jesus is not just God, but God the Son. His relationship to the Father, about whom he was rarely silent, begins to press in on you.

Without an articulated trinitarian theology, evangelicals can develop a bad habit of assigning all of God's work to Jesus: to think of him as the creator, the savior, the sanctifying indweller, the speaker of the Old Testament oracles, and so forth. Now, since the outward works of the Trinity are undivided, you can always find some way in which those statements are true. But they are often symptoms of Father-forgetfulness and Spirit-neglect, rather than indicators of healthy Christ-centredness. If they're not based on a robust understanding of the Trinity, they can lead on to actual errors: the disordered idea that Jesus is my heavenly Father, that he adopts me as his son, and so on. With the Trinity in place, all the bits and pieces of understanding fall into line and start making sense.

Should Christians pray to the three persons of the Godhead distinctly, or to the one Godhead all at once, or both?

Both are permissible, but we should pray mostly to God the Father in the name of the Son and in the power of the Holy Spirit. Learning to pray with more trinitarian specificity should be an invitation to go deeper into the biblical pattern of life and thought, not a conversion to some new thing.

In any given church, you'll have people at different stages of their understanding of trinitarian prayer, which leads to some awkwardness. We've all heard prayers that start out, “Heavenly Father,” and then within a couple of sentences are saying, “Thank you for dying on the cross for us.” Or prayers that start, “Dear Jesus” and move on to “thank you for sending your Son to save us.” What's going on here? Probably not outright heresies (patripassianism in the first case, some sort of Jesus-modalism in the second). Probably the person praying has been mentally focused on one person of the Trinity initially, and has shifted his or her attention to another person a few seconds later, without bothering to adjust all the other parts of the prayer or to vocalize a transition. Anybody in the congregation who is more fluent with trinitarian theology will hear something that sounds alarming. But I doubt that the person praying would fail a simple theology test if you stopped them and administered one (which, by the way, please don't).

As for praying to the Son and the Holy Spirit, that is also good, but it's best to follow the biblical proportions: praying mostly to the Father in the name of the Son and the power of the Holy Spirit. The rule is that you can pray to any person who is God, so you have three options, or four if you're letting yourself think vaguely about “God” and using it without making any mental trinitarian distinctions.

Suppose you are sharing the gospel with a postmodern person who does not believe in anything absolute or transcendent. How might the Trinity be a resource to your presentation of the gospel?

Sometimes postmodern commitments can bring with them a compensating virtue: people who don't believe in absolutes are often attentive to and attracted by particularity, by oddness, by quirkiness in the details. To such a mind, the doctrine of the Trinity has the merit of sounding strange (which, remember, is good). It doesn't sound like God in general, or some kind of self-evident theism. But it also doesn't sound quite random enough to be one of the lush polytheisms that can find mythological space for anything you want to worship. In dialogue with a postmodern person, I would lean into the sheer oddness of trinitarian monotheism.

There's a chance they'll think, That's strange, but it's strange like real life is strange. Perhaps it's right. Before he became a Christian, C. S. Lewis was drawn to this very aspect. In Mere Christianity he wrote,

That is one of the reasons I believe Christianity. It is a religion you could not have guessed. If it offered us just the kind of universe we had always expected, I should feel we were making it up. But, in fact, it is not the sort of thing anyone would have made up. It has just that queer twist about it that real things have.

So that would be a fruitful place to try for connections. Of course eventually anybody who denies absolutes or transcendent truths, and yet confesses Christ, is going to have to figure out how to confess the lordship of Christ over all things.

What might evangelicals learn from our Eastern Orthodox friends about the Trinity? Where should we be cautious regarding Eastern Orthodox teaching on the Trinity?

If evangelicals are suffering from a kind of timidity about being explicitly trinitarian, they can get a corrective blast by reading Eastern Orthodox writing or visiting an Orthodox church service. What you'll read or hear there is pretty much the polar opposite from embarrassment about the doctrine. In fact, it's about as ostentatious a parading of the extrabiblical technical terminology of the fully developed doctrine as you could imagine. You can hear prayers that say “Glory to the holy, consubstantial, life-creating, and indivisible Trinity,” or “to the Most Holy and Blessed Trinity, one in three and three in one, undivided and indivisible” and so on. Add the smells and bells of the incense and music and you definitely get the impression of an intentional liturgical immersion in this doctrine. I wouldn't want to settle in there, but as an antidote to trinitarian timidity it can be a real tonic.

The important Protestant differences with Eastern Orthodoxy lie elsewhere, in pretty obvious places: in the doctrines of Scriptural authority and of salvation by grace alone through faith alone. Those solas don't budge. But on the Trinity, there is such wonderful and substantial agreement that I'm all for throwing an ecumenical party around that doctrine.

What are some resources that someone could use to learn more about the Trinity?